Kathy Griffin's Asst.: I Lost 'An Olsen Twin'

When Tiffany Rinehart moved to Los Angeles to work as comedian Kathy Griffin's assistant, the job came with more than she had bargained for. Griffin was shooting her hit Bravo reality show "My Life on the D List," and Rinehart was soon making regular appearances.

The fun of suddenly being on TV was overshadowed by another concern, Rinehart said.

"I started watching it, and I'm like, Wow I'm fat! And I need to do something about it."

Watch this and other weight-loss stories on "20/20: Half Their Size" Friday at 10 p.m. ET

Rinehart decided not just to slim down but to get healthy, and began the slow process of losing weight through diet and exercise. She has lost more than 80 pounds.

"I've lost an Olsen twin, I like to say," Rinehart said. "They're about 80 pounds, right?"

Soon everyone, including her famous boss, was noticing her metamorphosis.

"I just started to notice that … she was leaving in workout clothes," Griffin said. "Then other people would say, 'Tiffany's lost a lot of weight.' But what was so smart about the way she did it was, she didn't come into the office one day and say, 'I'm gonna lose all this weight by this time.' She just started doing it."

Griffin knows how important being thin is in an industry that places enormous emphasis on how you look.

"I have to be thin and funny," Griffin said. "I could be fat and funny, but it would be harder to get gay men to appreciate my outfits."

Rinehart has lost more than 80 pounds but knows losing it is only half the battle.

"I think it's more of a lifestyle change and not just a fad diet," she said. "You have to commit to something for the rest of your life."

Her goal is to lose 100 total, and then to celebrate with a personal first.

"I never wore a two-piece bathing suit in my life, so I would like to one day do that."

Watch this and other weight-loss stories on "20/20: Half Their Size" Friday at 10 p.m. ET